Field of the Invention
The present invention relates to an electrophotographic image forming apparatus (hereinbelow, referred to as an image forming apparatus) and a cartridge detachably attachable to an apparatus main body of the image forming apparatus.
Description of the Related Art
The image forming apparatus described here is to form an image on a recording material using an electrophotographic image forming process. Examples of the image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (such as a laser beam printer and a light-emitting diode (LED) printer), a facsimile device, a word processor, and the like.
The cartridge is obtained by forming at least one of an electrophotographic photosensitive drum (hereinbelow, referred to as a photosensitive drum) as an image bearing member or a process unit (for example, a developer bearing member (hereinbelow, referred to as a developing roller)) acting on the photosensitive drum as a cartridge so as to be detachably attachable to the image forming apparatus.
There are a cartridge in which a photosensitive drum and a developing roller are integrally formed as a cartridge and a cartridge in which a photosensitive drum and a developing roller are separately formed as cartridges. Especially, the former one which includes the photosensitive drum and the developing roller is referred to as a process cartridge. Further, the latter one which includes the photosensitive drum is referred to as a drum cartridge, and the one which includes the developing roller is referred to as a developing cartridge.
The main body of the image forming apparatus is a remaining part of the image forming apparatus except for the cartridge.
Conventionally, image forming apparatuses adopt process cartridge methods in which photosensitive drums and process units acting on the photosensitive drums are integrally formed as cartridges, and the cartridges are formed to be detachably attachable to apparatus main bodies of the image forming apparatuses. According to the process cartridge methods, users can do maintenance of the image forming apparatuses by themselves without asking service persons, so that operability of the apparatuses can be significantly improved. Thus, the process cartridge methods are widely used in the image forming apparatuses.
For example, a developing device configured to be included in the process cartridge generally includes a rotatable charging member for applying charges to the photosensitive drum as a charging unit. A charging roller constituted of an elastic member such as rubber may be used as the charging member. If the elastic member such as rubber used for the roller remains abutting on the photosensitive drum from when it is manufactured to when a user starts using it, the elastic member may be deformed or cause a harmful effect on the photosensitive drum by a material seeping therefrom.
Thus, materials which are less subject to deformation or deterioration are conventionally selected as materials for the elastic member to be used in the process unit. In addition, a configuration is discussed in which a process unit and a photosensitive drum are delivered while maintaining in a separated state so as to expand a range of choices of available materials (Japanese Patent Application Laid-Open No. 2013-148629).
According to the invention described in Japanese Patent Application Laid-Open No. 2013-148629, separation members rotatably disposed on both end portions of a charging roller in an axial direction receive rotational force from the photosensitive drum and move from a first position for separating the photosensitive drum and the charging roller to a second position for abutting the photosensitive drum and the charging roller.
However, according to the configuration described in Japanese Patent Application Laid-Open No. 2013-148629, when the photosensitive drum is rotated, the separation members on the both end portions of the charging roller (the process unit) in the axial direction release a separated state of the charging roller with respect to the photosensitive drum (an image bearing member) at the same time. At that time, urging force is applied to the charging roller in a direction toward the photosensitive drum. When the separation member on the one end portion of the charging roller is rotated to release the separated state of the one end portion, a load is applied to the one end portion of the photosensitive drum in an opposite direction. When the separation member on the other end portion of the charging roller is rotated to release the separated state of the other end portion, a load is also applied to the other end portion of the photosensitive drum in an opposite direction. When these loads are applied at the same time, the load applied to the photosensitive drum opposite to a rotation direction is large.